Are you hungry? Tired? Sad? These experiences all rely on interoceptive sensations sent from the body to the brain. Interoceptive sensations can be experienced as a homeostatic requirement of the body (e.g., need for food, drink, rest), or as an affective state characterized as feelings of pleasure-displeasure and with some degree of arousal. In turn, affect seamlessly integrates into normal perception and decision-making. Moreover, because sources of affect go unrecognized everyday life, it is easy to misattribute affect to a spurious source, which can lead to unhealthy behavioral patterns (e.g., discomfort from an argument at work can be mistaken as discomfort of hunger, and can lead to overeating). Furthermore, in addition to being central to healthy mental life, interoception and affective processing are severely altered in many mental diseases such as somatoform disorders, depression, anxiety, and addiction, and in physical diseases involving neuropathy such as diabetes. Although facets of interoception and affective processing have been correlated, there is a critical lack of knowledge regarding causality in these relationships. Here, this barrier is addressed experimentally by using two training approaches to enhance interoceptive sensitivity in healthy young adults, and by comparing pre- and post-training measurements of three facets of affective processing: (i) affective judgment of evocative images, (ii) physiological reactivity in response to evocative images, and (iii) the extent to whic affective feelings are misattributed during person perception. To enhance interoceptive sensitivity, Study 1 uses traditional heartbeat detection training, whereas Study 2 uses a novel approach, real-time functional magnetic resonance imaging neurofeedback, to enhance brain activity in the right anterior insula, which is involved in interoception. In both studies, interoceptive sensitivity will be assessed pre- and post-training using a heartbeat detection task. Furthermore, to tailor interoceptive sensitivity training to the needs of each individual, Study 1 explores two sets of training instructions that may modulate whether an individual experiences interoceptive sensations as either (a) emotional feelings or (b) physical sensations (e.g., an individual with somatoform disorder has an unhealthy bias in experiencing physical sensations and hence would benefit from emotional feeling training). Accomplishing these aims will inform future research designed to explore novel interoception-intervention strategies (e.g., based on the two approaches studied here) to prevent, detect, or treat mental illness, to address psychological effects of physical illness, and to promote healthy behaviors in everyday life. PUBLIC HEALTH RELEVANCE: This project will begin to understand how an individual's ability to detect sensations from their body influences their mental reactions to those sensations. The mental reactions are central to normal perception, judgment, and decision making, and are altered in mental diseases such as somatoform disorders, depression, anxiety, and addiction, and in physical diseases involving neuropathy such as diabetes. Hence, this knowledge can help direct future research for prevention, diagnosis, and treatment.